Thats what I have to do when I do retrofits.

1) Heat oven to about 325 degrees, and make sure the bottom burner turns on.
2) Put headlights on a cookie sheet or something metal and flat enough for the headlights to fit into your oven
3) Leave in the oven for about 5-7min. and always keep an eye on them
4) Take lights out, (they're be hot) and pry the lense off with a flat head screw driver
5) Make sure you push the tabs back down, or when it cools, they'll stay upward.
6) When putting everything back together, use alot of clear silicone to make sure water doesn't get into your headlights and cause your lights to fog up when it rains

While your headlights are apart, you could paint the trim piece black, cause thats what alot of people seem to do now days